Study On Digital Chaotic Cipher Based On Dynamic Searching

With the development of the multimedia and digital communication, people deal with more and more information and communicate much more easily. For the security of information, it is necessary to protect it from eavesdropper. Although there are different demand for the cipher in different application, but security and speediness are the essential.Dynamic chaotic system with instability and noisy-like orbit is difficult to predict, some research have pointed out that there exists tight relationship between chaos and cryptography. But it is insecurity to construct the cryptography with chaotic system directly and for digital system, it is impossible to realize the real chaotic system because that the chaos is defined in continuous real number. In digital system, it is called digital chaotic system. This paper mainly studies the digital chaotic cipher and its application. On the basis of the chaos theory and current chaotic encryption technology, a systematic exposition is made. Based on the combination of chaos theory, dynamic searching and other related research, three new dynamic key encryption algorithms are designed. Chaotic sequence is generated from the chaotic map, after a series of transformations to get the dynamic key. Each block of the plaintext is encrypted as the key changes, which is called "once a secret key" encryption. The above algorithms make a perfect combination of sequence cipher and block cipher, and the simulation and analysis has verified the algorithm's excellent security performance. Specifically as follows:A block encryption algorithm using dynamic sequences generated by multiple chaotic systems. In this algorithm, several one-dimension chaotic maps generate pseudo-random sequences, which are independent and approximately uniform. After a series of transformations, the sequences constitute a new pseudo-random sequence uniformly distributing in the value space, which covers the plaintext by executing Exclusive-OR and shifting operations some rounds to form the cipher. This algorithm makes the pseudo-random sequence possess more concealment and noise like characteristic, and overcomes the periodic malpractice caused by the computer precision and single chaotic system.A sequence encryption algorithm based on chaotic switch control. This algorithm uses two chaotic systems to generate two chaotic key sequences respectively, which are selected by the chaotic pseudo-random binary sequence formed by Chebyshev polynomials iteration, called CSC (Chaotic Switch Controller) for encryption alternatively. This method not only can effectively resist cipher-text-only attack but also chosen-plaintext attack, which improves the security encrypted by a single chaotic sequence.A feedback chaotic cryptographic method based on piecewise linear chaotic maps. In this algorithm, a set of piecewise linear chaotic maps is defined and iterated to form a chaotic orbit. In order to avoid the degradation of piecewise linear chaotic maps under finite computing precision, a variant is employed to extract the key string from the chaotic orbit, which is used to instruct the shift operation on the message. Moreover, to enhance the security of the algorithm and resist the known plaintext attack, a feedback scheme is introduced to the message, in which the plaintext block and the former cipher block are mixed by means of the bit-wise XOR operations. Through several rounds of shift operations, the diffusion and confusion are well met. The results of simulation experiments and security analyses indicate that this encryption system not only has a large key space but also has a very sensitivity with respect to the secret key and the original message.